This application claims the benefit of Japanese Patent Application No. 2001-081452, filed on Mar. 21, 2001, the entirety of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates in general to a vibration damping bushing and an assembly including the bushing, and more particularly to a mechanism for assembling the bushing and a mounting bracket together so as to improve the durability of the bushing.
2. Discussion of Related Art
A vibration damping bushing having a generally cylindrical shape has been employed for various applications, such that the bushing is interposed between two members, for connecting these members in a vibration damping manner. For example, such a generally cylindrical vibration damping bushing includes an elastic body formed of a rubber or elastic material and having a bore through which there is inserted a shaft member connected to one of the two members indicated above. The elastic body has an outer flat mounting surface extending in its axial direction (in which the bore extends). The bushing is connected to the other of the two members through a mounting bracket such that the elastic body is fixed to the mounting bracket at the above-indicated outer flat mounting surface. For instance, the generally cylindrical vibration damping bushing is used in an automotive vehicle, as a stabilizer bushing for elastically connecting a stabilizer bar to a body of the vehicle in a vibration damping fashion.
In the case of the stabilizer bushing, the bushing is fixed to a frame of the vehicle body through the mounting bracket, such that the bushing and the mounting bracket are fixed together as a unit. To this end, the bushing is provided with an integrally formed projection for insertion through a mounting hole formed through the mounting bracket, so that the bushing and the mounting bracket constitute an assembly.
Described in detail by reference to FIG. 9 showing a vibration damping bushing in the form of a stabilizer bushing 2, the bushing 2 consists of an elastic body 3 formed of a rubber material and having a generally cylindrical shape in transverse cross section, with a center bore 2a formed therethrough so as to extend in its axial direction, so that a stabilizer bar extends through the center bore 2a. Described more precisely, the outer profile of the elastic body 3 in the transverse cross section consists of an upper semicircle and a lower rectangle, which cooperate to take the form of a tunnel or a barrel-roof or Nissen hut, as shown in FIG. 9. The elastic body 3 has a lower flat mounting surface 2b extending in the axial direction, and an internal slit 2c which permits the stabilizer bar to be inserted into the center bore 2a in the radial direction of the center bore 2a. The elastic body 3 of the stabilizer bushing 2 has an integrally formed mounting projection 4 extending downwards from an intermediate portion of the lower flat mounting surface 2b. The mounting projection 4 has a frusto-conical head for insertion through a mounting hole 8 formed through an intermediate part of a top wall of a U-shaped portion of a mounting bracket 6. The top wall of the mounting bracket 6 has an upper bearing surface 6a for contact with the mounting surface 2b of the stabilizer bushing 2 (elastic body 3), when the stabilizer bushing 2 is fixed to the mounting bracket 6, with the mounting projection 4 being inserted through the mounting hole 8 with elastic deformation of the frusto-conical head of the projection 4, such that the shoulder surface of the mounting projection 4 which is adjacent to the frusto-conical head is held in contact with the edge of the lower open end of the mounting hole 8, as indicated in FIG. 10. Thus, the stabilizer bushing 2 and the mounting bracket 6 are fixed together as a unit or assembly, which is subsequently fixed to the vehicle body.
While the stabilizer bushing 2 is installed on the vehicle body, with the assembly of the stabilizer bushing 2 and the mounting bracket 6 being fixed at the mounting bracket 6 to a suitable member of the vehicle body, however, the elastic body 3 suffers from insufficient durability due to stress concentration on a portion of the mounting surface 2b around the fixed end of the mounting projection 4 inserted through the mounting hole 8 formed through the upper bearing surface 6a of the mounting bracket 6, when a load acts on the stabilizer bushing 2 in a direction toward the bearing surface 6a due to a relative displacement between the stabilizer bar inserted through the center bore 2a of the stabilizer bushing 2 and the member of the vehicle body to which the mounting bracket 6 is fixed. The stress is concentrated on the portion of the mounting surface 2b around the fixed end of the projection 4, in the presence of the mounting hole 8, since the above-indicated portion of the mounting surface 2b is located adjacent to the edge of the upper open end of the hole 8 and is forced into the upper end portion of the hole 8 upon application of the load on the elastic body 3 in the direction toward the bearing surface 6a. Accordingly, the elastic body 3 tends to suffer from cracking at the portion of the mounting surface 2b around the fixed end of the mounting projection 4, leading to a risk of fracture of the projection 4 during the use of the stabilizer bushing 2 for a long time.
It is therefore a first object of the present invention to provide a vibration damping bushing having improved durability, without a risk of cracking or other damages due to a load acting on the bushing in a direction toward a mounting bracket. A second object of this invention is to provide an assembly of a vibration damping bushing and a mounting bracket, which assembly is improved in its durability without a risk of such damages of the bushing as described above.
The first object indicated above may be achieved according to a first aspect of this invention, which provides a vibration damping bushing including an elastic body of generally cylindrical shape formed of an elastic material and having a bore through which there is inserted a shaft member whose vibration is to be damped, and an outer mounting surface which extends in an axial direction of the elastic body and at which the elastic body is fixed to a mounting bracket, the vibration damping bushing comprising a plurality of engaging jaws formed integrally with the elastic body, on respective peripheral portions of the outer flat mounting surface of the elastic body, such that the engaging jaws extend from the mounting surface and are elastically engageable with respective engaging portions of the mounting bracket, so that the elastic body is fixed to the mounting bracket.
In the vibration damping bushing constructed as described above according to the first aspect of the present invention, the engaging jaws of the elastic body are not formed on a central portion of the outer flat mounting surface, but are formed on respective peripheral portions of the mounting surface, for engagement with the respective engaging portions of the mounting bracket. Accordingly, a bearing surface of the mounting bracket for contact with the mounting surface of the elastic body of the present bushing does not have a mounting hole which would cause a stress concentration on the mounting surface of the elastic body, due to a compressive load acting on the bushing fixed to the mounting bracket, upon application of a vibrational load between the shaft member inserted through the bushing and the mounting bracket. The engaging jaws are held in engagement with the respective engaging portions of the mounting bracket, under elastic forces of the engaging jaws owing to the elasticity of their elastic material, which elastic forces act on the surfaces of the engaging portions in a lateral direction parallel to the bearing surface, such that the engaging jaws are freely movable relative to the mounting bracket in the lateral direction away from the engaging portions, when the compressive load is applied to the present vibration damping bushing in the direction perpendicular to the above-indicated lateral direction. Thus, the engaging jaws are arranged to effectively prevent a stress concentration on the mounting surface of the elastic body and a consequent problem of cracking or other damage, thereby assuring improved durability of the bushing.
According to one preferred form of the vibration damping bushing of this invention, the outer flat mounting surface of the elastic body is a generally rectangular surface, and the plurality of engaging jaws consist of four engaging jaws formed at respective four corner portions of the generally rectangular surface. In this form of the bushing, the elastic body can be fixed to the mounting bracket with high stability, by engagement of the four engaging jaws with the respective four engaging portions of the bracket.
According to a second preferred form of the vibration damping bushing of the present invention, each of the engaging jaws includes a leg portion formed integrally with the elastic body, so as to extend from the outer flat mounting surface, and a hook portion extending from a free end face of the leg portion. In this case, the hook portion has a free end face inclined at a portion thereof on an inner side of the mounting surface, to provide a slant surface which is inclined toward the mounting surface as the slant surface extends inwardly of the mounting surface as seen in a plane parallel to the mounting surface, and the hook portion is engageable with a corresponding one of the engaging portions of the mounting bracket, by a relative movement of the engaging jaw and the corresponding engaging portion while the slant surface is in sliding contact with a surface of the corresponding engaging portion. The engaging jaws each including the leg portion and the hook portion can be easily brought into engagement with the respective engaging portions of the mounting bracket, thereby facilitating an operation to assemble the vibration damping bushing and the mounting bracket into an assembly.
In one advantageous arrangement of the second preferred form of the bushing described above, each engaging jaw further includes a reinforcing block formed integrally with the elastic body and the leg portion, so as to reinforce the leg portion, and the hook portion is formed on only the free end face of the leg portion. In the presence of the reinforcing block formed integrally with the leg portion, the leg portion is effectively reinforced so as to maintain the engaging jaw in engagement with the corresponding engaging portion of the mounting bracket with the elasticity of the leg and hook portions as well as the elasticity of the reinforcing block.
According to a third preferred form of the vibration damping bushing of the invention, the elastic body of generally cylindrical shape has an outer surface cooperating with the outer flat mounting surface to define an outer profile as seen in a plane perpendicular to the axial direction of the elastic body, and the elastic body further has an internal slit formed therethrough in a radial direction thereof, so as to extend in parallel with the outer flat mounting surface, between an inner circumferential surface of the bore and the above-indicated outer surface. The internal slit is formed over an entire axial length of the elastic body. This internal slit permits the shaft member to be fitted into the bore in the radial direction, such that the portions of the elastic body which define the slit are elastically deformed in the opposite directions so as to generate an inlet opening which communicates with the bore and which is large enough to permit the shaft member to be forced into the bore in the radial direction
The vibration damping bushing of the present invention is advantageously used as a stabilizer bushing on an automotive vehicle. In this case, a stabilizer bar provided as the shaft member is inserted through the bore of the elastic body of the stabilizer bushing.
According to a fourth preferred form of the vibration damping bushing of the invention, the plurality of engaging jaws of the elastic body are positioned relative to each other and dimensioned such that the engaging jaws are elastically deformed in sliding contact with surfaces of the engaging portions of the mounting bracket, when the elastic body and the mounting bracket are moved toward each other each other in a direction perpendicular to the outer flat mounting surface, for engagement of the engaging jaws with the respective engaging portions.
The second object indicated above may be achieved according to a second aspect of the present invention, which provides an assembly consisting of a vibration damping bushing according to the first aspect of this invention described above, and a mounting bracket having a plurality of engaging portions with which the plurality of engaging jaws of the elastic body are engageable, so that the elastic body and the mounting bracket are fixed to each other.
The assembly according to the second aspect of the invention has substantially the same advantages as the vibration damping bushing according to the first aspect of the invention described above. Further, the vibration damping bushing can be easily attached to a desired member such as the body of an automotive vehicle, by simply fixing the mounting bracket to the desired member, since the bushing and the mounting bracket constitute an integral assembly, that is, since the bushing has been firmly fixed to the mounting bracket.
According to one preferred form of the assembly according to the second aspect of this invention, the mounting bracket consists of a top wall portion and a pair of supporting leg portions, and the top wall portion has a bearing surface for contact with the outer flat mounting surface of the elastic body, and a generally rectangular shape as seen in a first plane parallel to the outer flat mounting surface. Each L-shaped supporting leg portion is L-shaped as seen in a second plane perpendicular to the above-indicated first plane, and the pair of L-shaped supporting leg portions extend from respective opposite ends of the top wall portion, in a symmetric relation with each other. Each L-shaped supporting leg portion consists of a vertical section extending downwards from a corresponding one of the opposite ends of the top wall portion, as seen in the second plane, and a horizontal section extending from a free end of the vertical section such that the horizontal sections of the pair of L-shaped supporting leg portions extend in opposite directions away from each other, in parallel with the top wall portion. In this instance, the plurality of engaging portions consist of four engaging portions formed at respective four corners of the generally rectangular top wall portion. In this form of the assembly, the vibration damping bushing is supported by the generally rectangular top wall portion of the mounting bracket, and the four engaging jaws formed on the mounting surface of the elastic body of the bushing are held in engagement with the respective engaging portions formed at the respective four corners of the generally rectangular top wall portion of the mounting bracket, so that the bushing can be firmly fixed to the mounting bracket.
According to one advantageous arrangement of the above-indicated preferred form of the assembly of the invention, the four engaging portions consist of four arcuate cutouts formed at the respective four corners of the top wall portion, and the plurality of engaging jaws of the elastic body consist of four engaging jaws which are held in engagement with the four arcuate cutouts, respectively, such that a free end portion of each of the four engaging jaws is partially located inwardly of a corresponding one of the arcuate cutouts as seen in the above-indicated first plane, and is held in contact with a part of a surface of the top wall portion opposite to the bearing surface, which part is adjacent to the corresponding one arcuate cutout. In this arrangement, the engaging jaws can be easily brought into engagement with the respective engaging portions in the form of the arcuate cutouts formed at the respective corner portions of the generally rectangular top wall portion of the mounting bracket, so that the bushing and the bracket can be easily assembled together.
The assembly according to the second aspect of this invention may consist of a stabilizer bushing as the vibration damping bushing, and the mounting bracket. In this case, the shaft member is a stabilizer bar provided on an automotive vehicle.